Yep hes telling the truth ^
You got to cycle a tank before adding fish, cycling basically means building of bacteria (good bacteria) which converts ammonia into nitrites, and nitrites into nitrates. Ammonia and nitrites are toxic to fish but nitrates are tolerable in normal amounts. Look up a guide on fishless cycling. cycling takes normally around 2 weeks to a month.
I wouldn't start with catfish if its going to be your first fish, but in the end its your choice. Some smaller catfish are corydoras, otocinclus, or raphael catfish, these are hardy as well.
I would suggest trying to sustain a 10 gallon tank first, they are a good size and not at all that expensive, then if you are still interested and committed you can move onto larger tanks, and larger fish.